docs: def get_idp_sso_supported_bindings(idp_entity_id=None, config=None):
      """Returns the list of bindings supported by an IDP
      This is not clear in the pysaml2 code, so wrapping it in a util"""
      if config is None:
          # avoid circular import
          from djangosaml2.conf import get_config
          config = get_config()
      # load metadata store from config
      meta = getattr(config, 'metadata', {})
      # if idp is None, assume only one exists so just use that
      if idp_entity_id is None:
          # .keys() returns dict_keys in python3.5+
          try:
              idp_entity_id = list(available_idps(config).keys())[0]
          except IndexError:
              raise ImproperlyConfigured("No IdP configured!")
      try:
          return meta.service(idp_entity_id, 'idpsso_descriptor', 'single_sign_on_service').keys()
      except UnknownSystemEntity:
          return []